This invention relates to a method of reducing the frost heaving that is caused by freezing of ground.
Artificial freezing of ground is a method of thermal soil solidification by freezing of the ground water, and it is employed to stop spring water and to harden soft ground. However, the freezing process causes two undesirable phenomena; i.e., frost heave and frost boils (subsidence). If freezing and thawing cycle of the soft ground is repeated more than twice, frost heaving and subsidence vary widely with each repeated run even if the frost-penetration rate and the effective stress of the ground are perfectly equal to each other. This indicates that the soft ground has no reproducibility of frost action in repetition of the freezing and thawing cycle. It is also known that excessive subsidence takes place during the thawing period in the first cycle of freezing and thawing.
Such phenomena of frost heave and subsidence are mostly attributable to fine grain size and high water content of soil constituting such soft ground and its small precompression stress. In other words, examining the particle size distribution curve of the soil constituting such soft ground, it is found that such soil rarely contains more than 10% of sand and gravel components with grain size of greater than 70 microns in diameter. Usually, the silt and clay components account for more than 90%. Such fine particle soils have strong water absorptivity on account of capillarity thereof and hence are high in water retainability so that the ground maintains high water content unless it is subjected to a greater stress than its own weight and is given any chance of drying throughout its history from formation of the ground up to date. Therefore, such soft ground is immediately consolidated and reduced in volume.
If a greater load than its precompression stress, which is usually less than 1 kg/cm.sup.2, is applied to the ground and if water is absorbed at the freezing front during the freezing, the pore water pressure of soil existing forward of the freezing front drops to increase the effective stress. This causes further consolidation and shrinkage of the soil. This accelerates the phenomenon of frost heave and subsidence upon freezing and thawing of the ground. Therefore, in order to minimize the frost heaving and subsidence in the prosecution of the artificial ground freezing, the initial frost heaving has to be suppressed.
It is accordingly an object of the present invention to reduce frost heave encountered not only in artificial ground freezing but also in the northern latitude where seasonal freezing and thawing of the ground takes place. The method of this invention accomplishes this object by increasing the viscosity of the pore water in the ground through the injection of a liquid chemical.